Vapor recovery using a plurality of progressively absorbent beds connected in series

ABSTRACT

A vapor recovery system for the controlled adsorption and desorption cycling of fuel vapors in an internal combustion engine comprising at least two vapor adsorbent beds connected in series to the fuel bowl of the engine carburetor and to the fuel tank with the adsorbent bed nearest to the source of fuel vapor becoming the most saturated during an adsorption cycle; and, throttle-controlled valve conduits connecting the absorbent beds to the fuel-air induction conduit of the carburetor whereby the least loaded adsorbent bed is purged during low engine loads but, as the throttle is opened to the full open position, all of the adsorbent beds will be purged.

United States Patent 3,352,294 11/1967 Biller et a1.

Joseph T. Wentworth Royal Oak, Mich.

Oct. 1, 1969 Apr. 20, 1971 General Motors Corporation Detroit, Mich.

Inventor Appl. No. Filed Patented Assignee 123/136 ....F02m 25/08 FieldofSearch 123/136, 119 (B), 121

References Cited UNITED STATES PATENTS 3,515,107 6/1970 Joyce ABSTRACT:A vapor recovery system for the controlled adsorption and desorptioncycling of fuel vapors in an internal combustion engine comprising atleast two vapor adsorbent beds connected in series to the fuel bowl ofthe engine carburetor and to the fuel tank with the adsorbent bednearest to the source of fuel vapor becoming the most saturated duringan adsorption cycle; and, throttle-controlled valve conduits connectingthe absorbent beds to the fuel-air induction conduit of the carburetorwhereby the least loaded adsorbent bed is purged during low engine loadsbut, as the throttle is opened to the full open position, all of theadsorbent beds will be purged.

' IIIIIIIII YPATENTED mu m 3.575; 152

I N VEN TOR.

A T TO/QNEY It is well known that vapors and gases evolved from internalcombustion engines contribute to the present day problem of airpollution. This air pollution problem is due in part to the fact that inthe past it has been customary to vent the fuel tank, and at times, thefuel bowl of the carburetor to the atmosphere, thus permitting theemission of hydrocarbon vapor into the atmosphere. These evaporativehydrocarbon emissions may be categorized as follows: carburetor bowlrunning losses, carburetor hot soak losses, tank running losses, andtank diurnal cycle losses. Carburetor running losses may occur duringperiods of engine operation due to the warming of the carburetor bowl bythe engine. I-lot soak is the condition achieved after a warmed-up caris stopped and its engine turned off, bringing about high underhoodtemperatures to effect the rapid vaporization and loss to the atmosphereof some of the fuel stored in the carburetor fuel bowl. Tank runninglosses are aggravated by the flow of heated air passing the gasolinetank which is usually mounted in the rear of the vehicle. The tankdiurnal cycle is the daily cyclic variation in temperature which causestank breathing and the resultant loss of vapor even though the vehicleis at rest.

In an effort to reduce the hydrocarbon emissions from the fuel system,various evaporative loss control devices have been proposed whereby, forexample, a canister filled with a suitable adsorbent material, such asactivated charcoal, is used to adsorb the hydrocarbon vapor when theengine is not in operation. Then, when the engine is operated, means areprovided to effect desorption or purging of the vapors from theadsorbent material so that these vapors can then be fed to thecombustionchambers of the engine for consumption therein. Also, duringengine operation, the running losses from both the tank and carburetorare being consumed as they are generated. This approach has workedsuccessfully to reduce hydrocarbon emissions, but under certain engineoperating conditions, the introduction of both the stored and currentlygenerated hydrocarbon vapors for consumption in the engine has eitheraffected engine operation or has caused an increase in the exhaustemission of unburned hydrocarbon.

To help overcome this latter problem, it has been proposed to use a flowcontrol valve to shut off the feedback of the stored hydrocarbon vaporsat engine speeds equivalent to roadload speeds below about 30 m.p.h.,but this then greatly increases the time required to effect a completedesorption cycle so that complete reactivation of the adsorbent materialmay not be accomplished under many short intown trips. Under suchconditions, it then would be possible after a number of engine-operatingcycles of this type to have the adsorbent material become saturated, sothat further vapor losses from the fuel could not be adsorbed resultingin the direct venting of hydrocarbon vapors to the atmosphere.

It is, therefore, the principle object of this invention to improvevapor recovery systems whereby desorption of the vapor can beaccomplished in a shorter time and with less effect on the air-fuelratio of an engine than previously known systems.

Another object of this invention is to improve vapor recovery systemsfor an internal combustion engine to effect a more closely controlledadsorption-desorption cycling whereby to trap hydrocarbon vapors whichmight otherwise be lost to the atmosphere, and to then feed thesehydrocarbon vapors to the engine in such a manner so as to have aminimum effect upon engine operation and minimum increase in emission ofunburned hydrocarbon from the exhaust.

These and other objects of the invention are attained by means of avapor recovery system for an internal combustion engine having at leasta first adsorbent bed and a second adsorbent bed, connected in series toeach other, with a vent to atmosphere extending from the first adsorbentbed, this vent line preferably terminating within the induction airflowpath in the air cleaner of the carburetor for the engine. When theengine is off, vent lines from the carburetor float bowl and the fueltank deliver gasoline vapor mixtures to the adsorbent bed, the ventlines being connected directly to the second adsorbent bed with the flowof vapor then being from the second bed to the first bed, whereby thesecond bed will become more saturated with the vapor than the first bed.Both the first and second adsorbent beds are connected by athrottle-controlled valve conduit means to the fuel-air inductionconduit of the engine carburetor whereby induction airflow through thecarburetor will cause air to move through either the first bed or thefirst and second beds, depending on the throttle setting to effectdesorption of the vapor from the adsorbent beds. This conduit and theconduit connected to the vent lines from the carburetor fuel bowl arecontrolled by suitable valves to direct routing of the vapors accordingto whether or not the engine is in operation.

For a better understanding of the invention, as well as other objectsand further features thereof, reference is had to the following detaileddescription of the invention to be read in connection with theaccompanying drawings, wherein:

FIG. 1 is a schematic view of a portion of an engine fuel systemincorporating the vapor recovery system of the invention when the engineis off;

FIG. 2 is a fragmentary view of FIG. 1 showing the condition of thevapor recovery system when the engine is in operation; and,

FIG. 3 is a fragmentary view of FIG. 1, but illustrating an alternatearrangement for venting the fuel tank during engine operation.

Referring to FIG. 1, the carburetor l0 and air cleaner assembly 11 areshown mounted on the intake manifold 12 of an engine, not shown. Thecarburetor 10 has a fuel-air induction conduit 13, a choke valve 14 andthrottle valve 15, the latter being connected in a conventional mannerto an accelerator pedal, not shown. A carburetor bowl 16 connectsthrough a discharge nozzle 17 with the venturi vent throat portion 18 ofthe air born 13 and contains a quantity of liquid fuel 20 to be mixedwith air passing the nozzle 17 for discharge into the intake manifold tobe consumed in the combustion chambers of the engine. A fuel pump 22, orsimilar device, supplies fuel through conduit 21 to the carburetor bowland in turn draws fuel from a fuel tank 24 through a conduit 23, thequantity of fuel being delivered to the carburetor bowl being controlledin the normal manner by a float valve or equivalent means, not shown.Fuel tank 24 is adapted to be filled through a filler pipe 25 normallyclosed by a nonvented cap 26. The air cleaner assembly 11 mounted on thecarburetor, includes the casing 30 with a suitable air inlet 31 theretoand a filter, such as paper filter 32 located in the air path betweenthe inlet 31 and the air horn l3.

As previously described, the effectiveness of the subject vapor recoverysystem is based upon a controlled adsorptiondesorption cycle, thedesorption cycle being phased through engine operation as controlled bythe carburetor. To accomplish this, the system includes two or moreadsorbent beds, connected in series to each other and to the fuelcontainer to be vented.

In the embodiment disclosed, the vapor recovery system is provided withthree adsorbent beds, each of the adsorbent ends containing an adsorbentmaterial 33, such as activated charcoal, positioned in canisters 34, 35and 36. Any suitable means, such as screens 37, may be used to retainthe adsorbent material within the canisters and allow aeriform fluid topass therethrough. Canister 34, containing the first adsorbent bed, isconnected by conduit 40 to canister 35 containing the second adsorbentbed, which in turn is connected by conduit 41 to canister 36, containingthe third adsorbent bed. Although these canisters can be vented in anysuitable manner, for the purposes of obtaining clean air during thedesorptive cycle, the vent line 42 connected to canister 34 terminateswithin the casing of the air cleaner to receive filtered air from thedownstream side of the paper filter 32.

The fuel tank 24 is vented to the adsorbent beds by conduit 43 incommunication with a valve casing 44 having a chamber 45 therein dividedby a valve seat plate 46 into two subchambers in communication with eachother by a vacuum relief valve 47 and a pressure release valve 48schematically represented for descriptive purposes and not described indetail since the specific configuration of these valves forms no part ofthe subject invention. Conduit 51 then connects this chamber to aconduit 52 in communication with canister 36, the latter also being incommunication by conduit 53, valve 54 and conduit 55 to the carburetorbowl 16 for the venting of fuel vapors released from the fuel remainingin the carburetor bowl after engine shutdown. The rotatable valveelement 56 of valve 54 is illustrated as being operated through thelinkage 57 and 58 by a solenoid 60 controlled by a suitable switch, suchas the ignition switch 61, connected to a suitable power source such asbattery 62. When the switch 61 is open and the engine is not inoperation, the valve element 56 is in the position shown in FIG. 1, withconduits 53 and 55 in communication with each other. During engineoperation, as shown in FIG. 2, the vapors from the carburetor bowl arevented by a conduit 63 directly to the carburetor and then to the enginefor consumption therein, the conduit 63 being connectable by the valveelement 56 to vent conduit 55 during engine operation, the opposite endof conduit 63 being in communication with the air horn of thecarburetor.

To effect controlled desorption in direct relation to the operatingconditions of the engine, the flow of air through the canisters and thento the carburetor is controlled by a distributor valve 65 and valve 66.Vent line 67 in communication with the venturi portion 18 of thefuel-air induction conduit is connected to valve 66, schematicallyrepresented here for descriptive purposes, having rotatable valveelement 68, which is also operated through the linkage 58 by solenoid60, previously described. Of course, other suitable means may be used tocontrol valves 54 and 66, such as a diaphragm activated by engine oilpressure. When the switch 61 is open and the solenoid 60 deenergized therotatable valve element 68 is in the position shown in FIG. 1, in whichit blocks the flow of air or vapor in line 67. When the ignition switch61 is closed as shown in FIG. 2, the rotatable valve element 68 connectsthe vent line 67 with conduit 70 which in turn is connected to theoutlet side of distributor valve 65. As shown schematically, distributorvalve 65 has a rotatable valve element 71 with a passage 72 therein forselective connection to conduits 80, 81 and 82 in communication withconduits 40, 41 and 42, respectively. The rotatable valve element 71 isillustrated as being operated through linkage 73 herein shown as coupledto the throttle valve 15, so that the displacement of the rotary valveelement 71 is directly related to the setting of the throttle valve, asdescribed hereinafter, so that the route of purging air through thevarious adsorbent beds can be controlled by the distributor valve.Furthermore, by having vent line 67 connected to the carburetor venturiportion 18, the airflow rate through the canisters increases inproportion with engineair consumption.

When the engine is not in operation, that is, when switch 61 is in theopen position, the various valve elements are in the position shown inFIG. 1. In this arrangement, fuel vapors emitted from the fuel bowl 16via conduit 55 and from the fuel tank 24 via conduit 43 are conveyedsuccessively through canisters 36, 35 and then 34, the latter beingvented to the atmosphere via conduit 42. However, assuming that theadsorbent material 33 in these canisters initially contains no adsorbedhydrocarbon vapors, then the vapors coming from the fuel bowl and thefuel tank will first enter canister 36 with most of the fuel vapor beingadsorbed therein. Of course, as the adsorbent material in canister 36becomes saturated, more of the hydrocarbon vapors will pass intocanister 35 whereby the majority of hydrocarbon vapors will be adsorbedtherein,

and again, as this adsorbent bed becomes saturated, the hydrocarbonvapors will then pass into canister 34 for adsorption therein. Thus, inessence, the adsorbent material in canister 36 will be the first to besaturated, after which the material in canister 35 will becomesaturated, and finally, canister 34 will become the least saturated. Ofcourse, it is assumed that the canisters 34, 3S and 36 will containsufficient adsorbent material so that under normal conditions, all ofthe hydrocarbon vapors given off from the fuel bowl and fuel tank willbe adsorbed so that no hydrocarbon vapors will be emitted to theatmosphere via vent line 42, with the bed in canister 36 being the mostsaturated with vapor while the bed in canister 34 would be the leastsaturated.

In this regard, although a sufficient quantity of adsorbent material iscontained in the system, each of the adsorbent beds need not be of equalsize, as shown, since design consideration may necessitate differentsized canisters for adequate location under the hood in relation toother equipment and, in addition, it is also realized that pore sizedistribution of the adsorbent may vary from one canister to another. Forexample, canister 36 may contain adsorbent material having a largeraverage pore size to retain the larger molecules of vapor while passingmore of the smaller molecules, such as C and C hydrocarbons, to beds 35and 34. Beds 35 and 34 may contain adsorbent material having somewhatsmaller average pore size which is well suited for the retention of Cand C hydrocarbons but which would hold heavier molecules tootenaciously for easy desorption, as is well known in the art.

When the engine is in operation, that is, when switch 61 is closed, thevalve elements 54 and 66 are moved to the positions shown in FIG. 2. Inthis arrangement, the carburetor bowl 16 is now vented directly to theair horn of the carburetor via conduit 55 and 63. In addition, rotatablevalve element 68 of valve 66 has now placed vent line 67 and conduit 70in communication with each other. With the engine in operation at idle,the throttle valve 15 would be in the position shown whereby, throughthe linkage 73, the rotary valve element 71 of distributor valve 65would then be in the position shown in FIG. 1, so that the passage 72therein, effects a connection between conduit 70 and conduit to permitair to flow only through canister 34. At idle, the engine airflow is atits lowest and idle air-fuel ratio is most sensitive to the amount ofair or vapor admitted through conduit 67. In the arrangement disclosed,however, he total flow through conduit 67 is also at its lowest, beingproportional to engine airflow. Further, the possibility of drawing ahigh concentration of vapor is reduced by purging only a lightly loadedportion of the total absorbent that is, the adsorbent bed in canister34. As engine speed is increased, the throttle valve 15 is openedfurther and as the purge airflow rate increases, the rotatable valveelement 71 of distributor valve 65 is moved to connected passage 72therein with conduit 81 so that the purge air flows through bothcanisters 34 and 35 and, at full throttle, passage 72 would be incommunication with conduit 82, with purge air then flowing through allof the canisters. Thus, the distributor valve is used to control theflow of purge air to more saturated adsorbent beds as the engine speedand purge airflow rate is increased, where engine air-fuel ratio is lesssensitive to the added vapor. With this system, better use is made ofthe purge air which the engine can tolerate. Purging progresses at thefull range of engine operation, which shortens the length of timerequired to prepare the adsorbent material for subsequent loading.However, the flow of purge air and also the concentration of vapor inthe purge stream are continuously modulated to minimize either excessiveleaning or richening of the overall air-fuel mixture entering the engineintake.

As previously described, the vapor outlet from the fuel tank 24 isprovided with both a vacuum relief valve 47 and a pressure relief valve48. As vapor pressure rises in the fuel tank, the pressure relief valveopens to allow vapor to flow to the adsorbent beds in canister 36, or ifthe engine is operating at full throttle, the vapor from the fuel tankis drawn directly into the carburetor. Because a pressure relief valveis sensitive to the differential pressures on opposite sides of thevalve element, the vapor pressure in the fuel tank will probably berelieved in spurts during periodic accelerations. This follows from thefact that the pressure depression at the venturi throat portion 18increases with throttle opening, and that by operation of thedistributor valve, purge air is progressively drawn through moreadsorbent material. Both of these factors tend to increase thedepression or partial vacuum on the downstream side, in terms of thedirection of flow of vapor from the tank, of the pressure relief valve.Assuming that the engine is a vehicle engine and that pressure in thefuel tank will build up uniformly while the vehicle is being driven innormal traffic situations including periodic accelerations,

most of the vapor from the fuel tank will be released directly into thecarburetor and will not be deposited on the adsorbent material. Since amajority of fuel tank vapors are evolved during driving periods, thesystem disclosed is helpful in keeping the required size of the totaladsorbent bed material to a minimum.

in some vehicles, the engine power-vehicle weight ratio may be largeenough so that the throttle is seldom opened enough to cause conduit 70to be directly connected to conduit 82 by means of valve 65. In suchcases, the linkage 73 between throttle valve and the valve element 71 ofdistributor valve 65 can be modified or the configuration of passage 72in the valve element 71 can be changed to effect a connection betweenconduit 70 and conduit 82 at a throttle setting less than full throttle,but at the higher engine speeds normal for the particular vehicle, toinsure the complete purging of canister 36 and more frequent directventing of vapor from the fuel tank to the fuel-air induction conduit ofthe carburetor during engine operation. Altemately, to effect directventing of vapor from the fuel tank to the fuel-air induction conduitduring engine operation but, independent of the speed thereof, a valvedconduit can be used to bypass the distributor valve as illustrated inthe embodiment of FIG. 3. As shown schematically, the conduit 51 and 91are selectively coupled by valve 92 to conduit 512 in communication withchamber 45, conduit 91 being connected to conduit 70. Valve 92, similarto valve 54, is operable by linkages 57a and 58 and routes fuel tankvapors to the adsorbent beds when the switch 61 is open, as before. Whenswitch 61 is closed, however, this added valve connects the outlet fromchamber 45 directly to conduit 70. In operation, the venting of the tankwill be similar to that already described except that it no longer willbe necessary to open the throttle fully in order to pass tank vaporsdirectly to the engine. Vapor passage can occur at any throttle opening,depending on the differential pressure across valve 48. Of course, thetank will still vent in spurts during periods of acceleration because ofthe factors controlling the depression on the downstream side of thepressure relief valve 48, as previously described.

lclaim:

l. A method for the recovery of fuel vapors from the fuel bowl of thecarburetor and fuel tank of an internal combustion engine comprising thesteps of: sequentially loading a plurality of beds of adsorbent materialwith fuel vapors while the engine is not in operation; sequentiallyunloading said beds with purge aeriform fluid in the reverse order ofloading during engine operation, and conducting the thus purged vaporsto the fuel-air induction conduit of said carburetor.

2. A method for the recovery of fuel vapors according to claim 1including the steps of venting fuel vapors from said fuel bowl directlyto the fuel-air induction conduit of said carburetor during engineoperation and venting fuel vapors from said fuel tank directly to thefuel-air induction conduit of said carburetor during periods ofhigh-speed engine operation.

3. A method of recovering fuel vapor from an engine fuel system, saidmethod comprising the steps of: sequentially storing fuel vapor from theengine fuel system in a plurality of adsorbent beds when the engine isnot operating, releasing the stored fuel vapor during engine operationby supplying aeriform fluid to the stored fuel vapor proportionate tothe air flow rate into the engine air intake with the fuel vapor releasebeing carried out in the reverse order of sequential fuel vapor storagewith the fuel vapor release responsive to air flow progressing from theleast loaded adsorbent beds during low air fiow to the more loadedadsorbent beds as the air flow increases, and conducting the releasedvapor to the engine air intake during engine operation and burning thereleased vapor therein.

4. A fuel vapor recovery system for an internal combustion engine havinga fuel reservoir and a carburetor containing a venturi, a throttle valverestricted throat and a fuel bowl, said system comprising a plurality offuel vapor storage means, conduit means connecting said fuel vaporstorage means with said fuel reservoir and said fuel bowl whenthe-engine is not operating to load said fuel vapor storage means in afixed vapor storage sequence, vent means connecting said fuel vaporstorage means to a source of aeriform fluid to release stored vapor,valved conduit means including distributor valve means connecting saidvapor storage means to said venturi of said carburetor when the engineis operating and, linkage means connecting said distributor valve tosaid throttle valve whereby said distributor valve controls the releaseof vapor from said fuel vapor storage means in the reverse order of saidfixed vapor storage sequence as a function of the throttle valvesetting. 7

5. A fuel vapor recovery system according to claim 4 wherein saidplurality of fuel vapor storage means comprises at least a firstcanister and a second canister each containing a quantity of adsorbentmaterial, said conduit means including a conduit connecting said firstcanister in series with said second canister, with said first canisterbeing connected to said vent means and said second canister positionedto first receive fuel vapor from said fuel reservoir and said fuel bowlwhen the engine is not in operation, said distributor valve beingconnected to said throttle valve to control the flow of aeriform fluidthrough said first canister when the engine is operating at idle and toeffect the flow of aeriform fluid through said first canister and saidsecond canister when said throttle valve is opened during higher speedengine operation.

6. A fuel vapor recovery system according to claim 4 wherein saidconduit means includes a pressure relief valve and a vacuum relief valvepositioned between said fuel reservoir and said plurality of fuel vaporstorage means and wherein said valved conduit means includes a firstvalve to prevent the flow of fuel vapor to said venturi when the engineis not in operation and a second valve to convey vapor from said fuelbowl to the fuel-air induction conduit of said carburetor when theengine is in operation.

7. A fuel vapor recovery system for an internal combustion engine havinga fuel reservoir and a carburetor with a venturi and throttle valverestricted fuel-air induction conduit and a fuel well, said systemcomprising a plurality of vapor adsorption bed means, conduit meansconnecting said bed means in series with respect to each other and atone end to a source of aeriform fluid and at the other end to said fuelreservoir, first valve-controlled conduit means for selectively couplingsaid fuel well to said conduit means between said fuel reservoir andsaid adsorption bed means when the engine is not in operation and tosaid fuel-air induction conduit when the engine is in operation and,second valve-controlled conduit means including a distributor valveoperatively connected to said throttle valve for selectively couplingsaid adsorption bed means via said conduit means to said venturi inaccordance with the setting of said throttle valve when the engine is inoperation and to block the flow of vapor from said adsorption bed meansand said fuel reservoir to said venturi when the engine is not inoperation.

8. A fuel vapor recovery system according to claim 7 wherein saidplurality of adsorption bed means includes a first bed means, a secondbed means and a third bed means, said conduit means connecting saidfirst bed means at one end to a source of aeriform fluid and, at theother end, to said second bed means, said second bed means to said thirdbed means and said third bed means to said fuel reservoir, said secondvalvecontrolled conduit means including a first conduit connecting saiddistributor valve to said conduit means between said first bed means andsaid second bed means, a second conduit connecting said distributorvalve to said conduit means between said second bed means and said thirdbed means and a third conduit connecting said distributor valve to saidconduit means between said third bed means and said fuel reservoir.

9. A fuel vapor recovery system according to claim 8 wherein saidconduit means includes a pressure relief valve and a vacuum relief valvepositioned between said fuel reservoir and said third conduit.

10. A fuel vapor recovery system according to claim 9 further includingthird valve-controlled conduit means connected to said conduit meansbetween said vapor adsorption bed means and said fuel reservoir and tosaid second valve-controlled conduit means between said distributorvalve and said venturi, said third valve-controlled conduit meansincluding a control valve means to route vapor from said fuel reservoirto said vapor adsorption bed means when the engine is not in operationand to route vapor from said fuel reservoir to said venturi when theengine is in operation bypassing said vapor adsorption bed means.

2. A method for the recovery of fuel vapors according to claim 1 including the steps of venting fuel vapors from said fuel bowl directly to the fuel-air induction conduit of said carburetor during engine operation and venting fuel vapors from said fuel tank directly to the fuel-air induction conduit of said carburetor during periods of high-speed engine operation.
 3. A method of recovering fuel vapor from an engine fuel system, said method comprising the steps of: sequentially storing fuel vapor from the engine fuel system in a plurality of adsorbent beds when the engine is not operating, releasing the stored fuel vapor during engine operation by supplying aeriform fluid to the stored fuel vapor proportionate to the air flow rate into the engine air intake with the fuel vapor release being carried out in the reverse order of sequential fuel vapor storage with the fuel vapor release responsive to air flow progressing from the least loaded adsorbent beds during low air flow to the more loaded adsorbent beds as the air flow increases, and conducting the released vapor to the engine air intake during engine operation and burning the released vapor therein.
 4. A fuel vapor recovery system for an internal combustion engine having a fuel reservoir and a carburetor containing a venturi, a throttle valve restricted throat and a fuel bowl, said system comprising a plurality of fuel vapor storage means, conduit means connecting said fuel vapor storage means with said fuel reservoir and said fuel bowl when the engine is not operating to load said fuel vapor storage means in a fixed vapor storage sequence, vent means connecting said fuel vapor storage means to a source of aeriform fluid to release stored vapor, valved conduit means including distributor valve means connecting said vapor storage means to said venturi of said carburetor when the engine is operating and, linkage means connecting said distributor valve to said throttle valve whereby said distributor valve controls the release of vapor from said fuel vapor storage means in the reverse order of said fixed vapor storage sequence as a function of the throttle valVe setting.
 5. A fuel vapor recovery system according to claim 4 wherein said plurality of fuel vapor storage means comprises at least a first canister and a second canister each containing a quantity of adsorbent material, said conduit means including a conduit connecting said first canister in series with said second canister, with said first canister being connected to said vent means and said second canister positioned to first receive fuel vapor from said fuel reservoir and said fuel bowl when the engine is not in operation, said distributor valve being connected to said throttle valve to control the flow of aeriform fluid through said first canister when the engine is operating at idle and to effect the flow of aeriform fluid through said first canister and said second canister when said throttle valve is opened during higher speed engine operation.
 6. A fuel vapor recovery system according to claim 4 wherein said conduit means includes a pressure relief valve and a vacuum relief valve positioned between said fuel reservoir and said plurality of fuel vapor storage means and wherein said valved conduit means includes a first valve to prevent the flow of fuel vapor to said venturi when the engine is not in operation and a second valve to convey vapor from said fuel bowl to the fuel-air induction conduit of said carburetor when the engine is in operation.
 7. A fuel vapor recovery system for an internal combustion engine having a fuel reservoir and a carburetor with a venturi and throttle valve restricted fuel-air induction conduit and a fuel well, said system comprising a plurality of vapor adsorption bed means, conduit means connecting said bed means in series with respect to each other and at one end to a source of aeriform fluid and at the other end to said fuel reservoir, first valve-controlled conduit means for selectively coupling said fuel well to said conduit means between said fuel reservoir and said adsorption bed means when the engine is not in operation and to said fuel-air induction conduit when the engine is in operation and, second valve-controlled conduit means including a distributor valve operatively connected to said throttle valve for selectively coupling said adsorption bed means via said conduit means to said venturi in accordance with the setting of said throttle valve when the engine is in operation and to block the flow of vapor from said adsorption bed means and said fuel reservoir to said venturi when the engine is not in operation.
 8. A fuel vapor recovery system according to claim 7 wherein said plurality of adsorption bed means includes a first bed means, a second bed means and a third bed means, said conduit means connecting said first bed means at one end to a source of aeriform fluid and, at the other end, to said second bed means, said second bed means to said third bed means and said third bed means to said fuel reservoir, said second valve-controlled conduit means including a first conduit connecting said distributor valve to said conduit means between said first bed means and said second bed means, a second conduit connecting said distributor valve to said conduit means between said second bed means and said third bed means and a third conduit connecting said distributor valve to said conduit means between said third bed means and said fuel reservoir.
 9. A fuel vapor recovery system according to claim 8 wherein said conduit means includes a pressure relief valve and a vacuum relief valve positioned between said fuel reservoir and said third conduit.
 10. A fuel vapor recovery system according to claim 9 further including third valve-controlled conduit means connected to said conduit means between said vapor adsorption bed means and said fuel reservoir and to said second valve-controlled conduit means between said distributor valve and said venturi, said third valve-controlled conduit means including a control valve means to route vapor from said fuel reservoir to said vapor adsorption bed means when the engine iS not in operation and to route vapor from said fuel reservoir to said venturi when the engine is in operation bypassing said vapor adsorption bed means. 